1. Field of the Invention
The present invention is directed to a solvent cleaning system and, more particularly, is directed to a pulse vacuum extraction system and methodology for removing solvent from a cleaning vessel.
2. Discussion
Organic solvents and cleaning agents are used in various types of vapor degreasing and defluxing equipment to clean articles of manufacturer, deflux electronic circuit boards, and the like. The organic solvents generally used are volatile organic solvents.
Solvents have been recognized to contribute to the global warming phenomenon. In view of these damaging effects on the environment from solvents venting into the atmosphere, alternative drying methods are required to lower atmospheric emissions and operator exposure. Alternative cleaning and recovery methods are generally more expensive. The traditional incentives to reduce vapor loses because of cost and safety were enhanced with the global warming phenomenon. With the use of these cleaning solvents, new parameters were required for various regions in the degreaser tank to minimize degradation of the tank by these solvents during the extraction or drying cycle.
As a consequence of the enhanced desire to reduce vapor loses, many solvent cleaning system manufacturers rely upon the use of closed vessel cleaning systems. In such systems, rather than relying upon an open vat, bath, or other vessel as a container for the cleaning solvent, from which various costly and unsafe vapors can escape, manufactures have increasingly turned to the use of the closed cleaning systems. The product to be cleaned is placed inside the closed vessel which is then flooded with cleaning solvent solution. The solvent solution is then circulated to clean the product. Following the circulation process, the liquid solution is removed from the vessel. After the liquid solvent has been removed from the vessel, some liquid solvent will remain within the vessel in and among the product to be cleaned. Conventionally, the product will be dried and the vessel may be emptied by evaporating the liquid solvent into a gas and evacuating the solvent in the gaseous state from the vessel. This removes the liquid solvent from the vessel and also drys the product.
In conventional closed solvent cleaning systems, drying the product and removing the solvent from the closed vessel is accomplished by creating a vacuum within the vessel. Creating a vacuum lowers the boiling point of the solvent so that the solvent effectively evaporates into a gas which may then be evacuated from the closed vessel. Present solvent cleaning systems attempt to create a perfect vacuum, approximately 30 inches of mercury (Hg), within the cleaning vessel. Such a deep vacuum has several adverse affects. First, a deep vacuum causes the solvent to boil and may cause premature breakdown of solvents with stabilizers or additives. The broken down solvent attacks the interior of the cleaning vessel, eventually requiring that the cleaning vessel to be replaced. Because cleaning vessels are rather costly, breaking down the solvent in this manner is undesirable. Solvent breakdown is enhanced if water is present in the solvent, further attacking the interior of the vessel. Second, it has been shown that while a deep vacuum may ensure evaporation of the liquid solvent, the evaporated solvent lacks sufficient density to travel across the vessel and be removed from the vessel. Even though the entirety of the solvent may be evaporated by using a deep vacuum, gas residue from the solvent often remains in the cleaning vessel because the solvent gas lacks sufficient density to be moved from the cleaning vessel. Residual solvent in a gaseous state also creates a safety issue. When the operator opens the cleaning vessel to remove the cleaned product and to insert new product to be cleaned, exhaust fans which are activated upon opening the vessel may cause the evaporated solvent to escape in the direction of the operator. This poses a possible health issue to the operator.
Thus, it is an object of the present invention to provide a closed solvent cleaning system for substantially removing all solvent from the closed vessel with minimum solvent breakdown.